The Wiimote's accelerometers do have moving parts. Specifically, near-hair-thin components that measure the distance they travel between special "prongs", and how long it takes. That's why it can detect the force of your swing. However, given that the components are basically banging against each other, the hair-like components can potentially get caught under the grooves they travel between, particularly if you make a series of especially violent swings. Smacking the Wiimote like that would have the effect of jostling them loose.
I'd say it's a testament to the quality of parts in Nintendo products that this doesn't snap the accelerometer components off. Then again, maybe it does; I understand there's a number of them present, so one or two broken won't lead to a permanently motion-senseless Wiimote.
Sky Render - Sanity is for the weak.
